As Bob Dylan once sang: ‘The Times They Are a-Changin’. And filtration in cars has also changed a great deal, both in terms of technology and the way it is presented. Marcel Hofmeister, ‘part-time museum director’ at the MANN+HUMMEL filter museum in Ludwigsburg, takes us on a little journey into the past.
‘Egon saw a strange dance in a ray of light: a multitude of glittering specks were undulating in the air. ‘It’s all dust’, he thought, but was quite intrigued by what exactly it is that lingers in the air we breathe.
These words are what brought Egon to my attention. Egon was a filling station attendant and also the champion of the ‘MANN-FILTER filter service’, a series of technical papers on filtration in cars published in the early 1960s. He gave readers at the time an insight into the subtleties of filtration in cars. This came from a qualified source: After all, at the time, filling station attendants were not only responsible for filling cars with petrol and checking tyre pressure, but also for changing filter elements.
Nowadays, very few employees at MANN+HUMMEL are aware of Egon. I first heard about him myself when I was reading through old brochures and product descriptions in the MANN+HUMMEL filter museum in Ludwigsburg some time ago. As ‘part-time museum director’ (I deal with matters relating to engine air filtration for my day job), I wanted to learn more about the company history. Stories about Egon were very useful for better understanding the development of demands placed on vehicle air filters.
Demands have increased
Since the old MANN+HUMMEL filter plant was set up in 1941, a lot of work has been done on filtration including, in the example above, on engine air filtration. The basic requirements for an air filtration system have not changed since those days: i.e. preventing potentially damaging dirt and dust particles from entering the ambient air so that only clean air is supplied to the engine for combustion.
However, requirements have increased considerably since Egon’s days. In the 1960s, a separation efficiency of 99% was deemed necessary. This means that 99% of particles in the air of a specific size are eliminated. Nowadays, separation efficiencies of up to 99.98% are required for certain uses, such as in HGVs. This increase of ‘just 0.98 percent’ may seem small at first glance. However, the following simple example gives a clearer understanding of this improvement. If a filter element is loaded with 1,000 g of dust (a large air filter element for an HGV can take up to 3,000 g of dust), 10 g of dust would pass through the element based on a separation efficiency of 99%. In the 1960s, this meant that over the entire lifespan of an air filter element from fitting to replacement, 10 g of small particles passed through the element, which was completely acceptable for engines at the time.
With modern high-elimination media offering efficiency of 99.98%, the filter element is only unable to keep out 0.2 g of tiny particles (this amount corresponds to less than one tenth of a teaspoon), as opposed to 10 g. So dust passage is fifty times lower than it was in the sixties! Egon would probably be amazed by this.
Filtration – a matter of pressure
Although even higher separation efficiencies are possible, you have to keep pressure loss in mind. In this context, pressure loss is a measurement of the resistance met by the air when passing through the filter medium. Higher levels of pressure loss therefore mean that the engine can no longer ‘breathe as freely’. It’s therefore not enough to simply increase the density or thickness of the filter medium.
MANN+HUMMEL developers are focusing all their expertise on overcoming this apparent contradiction between high separation efficiency and low pressure loss. This ensures that the engine has a long service life and the vehicle also uses less fuel, thereby reducing its CO2 emissions.
As well as improving the separation efficiency, modern filter media also offer other advantages: The service life of the element can be increased with better filter media. While cellulose filter paper was once the only available option, fully synthetic media or media with nanofibres have now been available for years. This means that vehicles can cover greater distances with the same filter element, offering motorists an advantage in terms of cost.
Besides the filter itself, the filter housing and the pipes carrying the air flow also play a vital role. Indeed, all connected components must be coordinated with one another (we talk of air filter systems). While Egon knew the air filter as a black painted round housing made of sheet steel, these parts can often only be identified as ‘black plastic parts’ nowadays. However, a great deal of expertise and development work goes into ensuring that they are built, designed and produced to optimal standards: Extensive computer simulation and testing is required just to optimise air flow direction. This allows filter system pressure loss to be significantly reduced, among other things. As we have already mentioned, this helps to reduce fuel consumption and CO2 emissions, which in turn saves money and is good for the environment.
The air filter system is also partly responsible for vehicles’ acoustics, as the engine’s intake noise is reduced by the air filter. It is clear that a modern air filter system has a multitude of other functions to perform besides just filtration.
Hi-tech filtration solutions are essential
Since modern combustion engines are becoming increasingly complex due to measures such as downsizing, direct injection systems with high injection pressures and multiple supercharging in some cases, increasing demands are being placed on filtration. Air filter systems are being continually developed, as even tiny particles can be the proverbial ‘spanner in the works’.
So you shouldn’t be surprised if, in several years’ or decades’ time, you feel the same way as Egon when walking around a (filter) museum.